The main acceptor product of glucansucrases with D-mannose has not previously been identified. We used glucansucrases that form water-insoluble alpha-D-glucans to produce increased yields of acceptor products from D-mannose, and identified the major product as 6-O-alpha-D-glucopyranosyl-D-mannose. Glucan-sucrases that synthesize insoluble alpha-nu-glucans produced higher yields of the disaccharide compared to typical dextransucrases. Published by Elsevier Ltd.